With dwindling of oil resources and increasing of environment pollution, energy conservation and emission reduction have become the trend in the world. Accordingly, electric vehicles such as hybrid electric vehicle, plug-in hybrids, and pure electric vehicles, have emerged and increased gradually. During driving, electric vehicles release less carbon dioxide than traditional internal combustion engine vehicles, and pure electric vehicles even release zero carbon dioxide. Moreover, the electric vehicles have an advantage of high energy conversion efficiency. These make the electric vehicles be recognized as an important substitute of internal combustion engine vehicles in the future.
Lithium-ion battery is known as a high energy density battery, and its organic electrolyte are flammable. Besides, lithium is highly reactive. These result some safety defects of lithium-ion battery. As being used as power battery, lithium-ion battery needs high capacity and high output power which results the lithium-ion battery generates much heat during operation and causes potential safety hazard. Especially, if the lithium-ion battery is used under harsh condition, such as thermal shock, over-charge, over-discharge and short circuit, the active material and the electrolyte inside the battery will conduct chemical and electrochemical reactions, which produce a large amount of heat and gas. When the heat and gas accumulate to a certain extent, it may give rise to battery burst which allows the active material inside the battery contacting with air and then causes explosion. Consequently, it's very important to improve safety design of lithium-ion battery.
Chinese Application No. CN201120526633.8, entitled “Close-packing lithium-ion battery pack”, discloses a proposal of realizing uniform heat dissipation and flame retardant effect of lithium-ion battery. The battery pack includes a plurality of battery module, a plurality of spacing board, a plurality of aluminum separator, a plurality of aluminum cover and a bottom module cover. The spacing board and the aluminum separator separate battery cells from the battery modules, realizing requirements of omni-directional and uniform heat dissipation of the lithium-ion battery and overcoming a disadvantage of weak heat dissipation in a current battery pack. In addition, the close-packing lithium-ion battery pack is characterized by convenient manufacture and assembly, excellent heat dissipation efficiency, safety and reliability, and realizing a high-efficient continuous production procedure of the cell pack, and ensuring safety and reliability in application of the lithium-ion power cell effectively.
This proposal is beneficial of uniform heat distribution inside the battery pack, and transmitting heat to the aluminum separator is a relatively reasonable method. But it just works when the aluminum separator can meet the heat dissipation requirement of the battery pack before thermal runaway. The reason why thermal runaway occurs in the battery pack is that the heat can't be dissipated in time and accumulates in somewhere. That is to say, there are some limitations by using aluminum separators for heat dissipation, and it can't avoid the risk of thermal runaway completely.